sometimes difficult to distinguish Hipparkhos’ material from Ptolemy’s. Consequently, some
scholars have underemphasized the scale and nature of Ptolemy’s achievement, but gener-
ally a considerable degree of difference is now acknowledged between Ptolemy and Hip-
parkhos, in spite of important lines of dependence. Clearly Hipparkhos seems not to have
written a systematic astronomical treatise to prefigure the Almagest, but he instead did much
foundational work that Ptolemy would later use in his systematization of mathematical
astronomy. Considerable evidence suggests that Hipparkhos used both (Greek) geometrical
and (Babylonian) arithmetical methods in his astronomical calculations. Hipparkhos is
believed to have published a collection of eclipse observations spanning 600 years (thus
going back to the 8th c. BCE) and including much Babylonian material that Hipparkhos
himself may have collected in Babylo ̄n. Indeed, when Kugler discovered in 1900 that
Hipparkhos’ very precise value for the mean synodic month (in sexagesimal notation:
29; 31,50,08,20 days) was actually borrowed from the Babylonian “System B” for the Moon,
only then did we recognize the deep indebtedness of Greek mathematical astronomy to
Babylon. Hipparkhos’ published eclipse records were an invaluable resource for Ptolemy’s
lunar theory. Ptolemy’s solar theory is also deeply indebted to Hipparkhos, including the
wholesale use of his values for the lengths of the seasons and solar year.
Hipparkhos is perhaps best known for his discovery of the precession of the equinoxes,
the very slow (and very difficult to observe) movement of the equinoctial points relative
to the fixed stars. His fundamental work on parallax allowed accurate prediction of solar
eclipses for the first time. He is also known to have been innovative in developing astro-
nomical instruments, including a dioptra, an accurate star globe, and possibly even the plane
astrolabe.
Later writers praise Hipparkhos for his skill in astrology, and P (2.95) reports that no-
one had done so much as Hipparkhos to establish clearly the connection between human souls
and the stars. Unfortunately, however, virtually nothing of the details of his astrology survive.
He also seems to have written something on combinatoric logic, criticizing C.
His attested lost works include: On the Movements of the Solsticial and Equinoctial Points, On the
Length of the Year, On Intercalary Months and Days, On the Risings of the Twelve Zodiacal Signs, Treatise
on Simultaneous Risings, On Sizes and Distances, On the Moon’s Monthly Motion in Latitude, On Things
Carried down by their Weight, and Against the Geography of E (most of our know-
ledge of which comes from S). Hipparkhos also wrote on chords in 12 (implausibly
long) books, according to T A (In Ptol. Synt. 1.10). Two other titles
commonly found in modern sources, On the Length of the Month and On Matters Pertaining to
Straight Lines in the Circle, are essentially fabrications of Albert Rehm.
Ed.: K. Manitius, Hipparchi in Arati et Eudoxi phaenomena commentariorum libri tres (1894).
Neugebauer (1975) 274–343; G.J. Toomer, “Hipparchus and Babylonian Astronomy,” in E. Leichty
et al. (1988) 353–362; A. Jones, “The Adaptation of Babylonian Methods in Greek Numerical
Astronomy,” Isis 82 (1991) 441–453.
HIPPARKHOS OF NIKAIA